Structural characteristics of multilayered ni-ti nanocomposite fabricated by high speed high pressure torsion (Hshpt)

47PCCDI/2018 MANUNET 3 PN3-P3-302 grant number 99-2019It is generally accepted that severe plastic deformation (SPD) has the ability to produce ultrafinegrained (UFG) and nanocrystalline materials in bulk. Recent developments in high pressure torsion (HPT) processes have led to the production of bimetallic composites using copper, aluminum or magnesium alloys. This article outlines a new approach to fabricate multilayered Ni-Ti nanocomposites by a patented SPD technique, namely, high speed high pressure torsion (HSHPT). The multilayered composite discs consist of Ni-Ti alloys of different composition: a shape memory alloy (SMA) Ti-rich, whose Mf > RT, and an SMA Ni-rich, whose Af < RT. The composites were designed to have 2 to 32 layers of both alloys. The layers were arranged in different sequences to improve the shape recovery on both heating and cooling of nickel-titanium alloys. The manufacturing process of Ni-Ti multilayers is explained in this work. The evolution of the microstructure was traced using optical, scanning electron and transmission electron microscopes. The effectiveness of the bonding of the multilayered composites was investigated. The shape memory characteristics and the martensitic transition of the nickel-titanium nanocomposites were studied by differential scanning calorimetry (DSC). This method opens up new possibilities for designing various layered metal-matrix composites achieving the best combination of shape memory, deformability and tensile strength.publishersversionpublishe

Effects of Cold Rolling Deformation and Solution Treatment on Microstructural, Mechanical, and Corrosion Properties of a Biocompatible Ti-Nb-Ta-Zr Alloy

One of the most important requirements for a metallic biomaterial is the mechanical biocompatibility, which means excellent mechanical properties&mdash;high strength and fatigue strength, but low elastic modulus, to be mechanically harmonized with hard tissues. In order to improve the mechanical and biocompatible performance of the Ti-25.5Nb-4.5Ta-8.0Zr wt% alloy, the influence of cold plastic deformation and solution treatment on its properties were investigated. The Ti-25.5Nb-4.5Ta-8.0Zr wt% alloy was fabricated by melting in a cold crucible furnace (in levitation) and then subjected to several treatment schemes, which include cold rolling and different solution treatments. Microstructural and mechanical characteristics of specimens in as-cast and thermo-mechanically processed condition were determined by SEM microscopy and tensile testing, for different structural states: initial as-cast/as-received, cold rolled and solution treated at different temperatures (800, 900, and 1000 &deg;C) and durations (5, 10, 15, and 20 min), with water quenching. It was concluded that both cold rolling and solution treatment have important positive effects on structural and mechanical properties of the biomaterial, increasing mechanical strength and decreasing the elastic modulus. Samples in different structural states were also corrosion tested and the results provided important information on determining the optimal processing scheme to obtain a high-performance biomaterial. The final processing route chosen consists of a cold rolling deformation with a total deformation degree of 60%, followed by a solution heat treatment at 900 &deg;C with maintenance duration of 5 min and water quenching. By applying this thermo-mechanical processing scheme, the Ti-25.5Nb-4.5Ta-8.0Zr wt% alloy showed an elastic modulus of 56 GPa (5% higher than in the as-cast state), an ultimate tensile strength of 1004 MPa (41.8% higher than in the as-cast state), a yield strength of 718 MPa (40.6% higher than in the as-cast state), and increased corrosion resistance (the corrosion rate decreased by 50% compared to the as-cast state)

Evolution of Microstructural and Mechanical Properties during Cold-Rolling Deformation of a Biocompatible Ti-Nb-Zr-Ta Alloy

In this study, a Ti-32.9Nb-4.2Zr-7.5Ta (wt%) titanium alloy was produced by melting in a cold crucible induction in a levitation furnace, and then deforming by cold rolling, with progressive deformation degrees (thickness reduction), from 15% to 60%, in 15% increments. The microstructural characteristics of the specimens in as-received and cold-rolled conditions were determined by XRD and SEM microscopy, while the mechanical characteristics were obtained by tensile and microhardness testing. It was concluded that, in all cases, the Ti-32.9Nb-4.2Zr-7.5Ta (wt%) showed a bimodal microstructure consisting of Ti-&beta; and Ti-&alpha;&Prime; phases. Cold deformation induced significant changes in the microstructural and the mechanical properties, leading to grain-refinement, crystalline cell distortions and variations in the weight-fraction ratio of both Ti-&beta; and Ti-&alpha;&Prime; phases, as the applied degree of deformation increased from 15% to 60%. Changes in the mechanical properties were also observed: the strength properties (ultimate tensile strength, yield strength and microhardness) increased, while the ductility properties (fracture strain and elastic modulus) decreased, as a result of variations in the weight-fraction ratio, the crystallite size and the strain hardening induced by the progressive cold deformation in the Ti-&beta; and Ti-&alpha;&Prime; phases